Paper machines for manufacturing soft paper with high bulk are known through a number of patent specifications. Usually a texturing wire or a texturing felt is used, which, together with the formed paper web, runs through a press nip in which the paper web is pressed into the texturing wire and thus acquires a textured pattern on one of its sides. Paper machines with such texturing wires and press nips are described in U.S. Pat. No. 3,301,746, U.S. Pat. No. 3,537,954, U.S. Pat. No. 4,309,246, U.S. Pat. No. 4,533,437, U.S. Pat. No. 5,569,358, U.S. Pat. No. 5,591,305 and WO 91/16493 (corresponding to SE-466 063). The disadvantage with paper machines in accordance with these patents is that the dewatering in the press nip is relatively low, so that the dry solids content of the paper web is low when the paper web is transferred to the drying cylinder, which results in the output of the paper machine being relatively low.
U.S. Pat. No. 4,849,054 describes a machine for manufacturing a textured fibrous web with high bulk, where the fibrous web is pressed in a single-clothed roller press having a transfer roll, which, together with a texturing wire, defines a nip at a transfer point for the web. The press dewaters the web to a dry solids content of 30 to 50 percent. At the transfer point, the texturing wire runs around a stationary suction pipe, which has a slot opening facing the nip, the slot opening being sufficiently wide that the fibrous web is not compressed when it runs through the nip. By means of the suction from the suction pipe via the slot opening, the fibrous web is transferred to the texturing wire and formed in accordance with the surface of the texturing wire facing the fibrous web, which surface has a three-dimensional pattern. Before the transfer point, the fibrous web has a speed which is greater than the speed of the texturing wire. The roller that carries the fibrous web up to the non-compressing nip has a smooth surface and it is well known that, in practice, there are problems associated with transferring a fibrous web that has been pre-pressed to a dry solids content of 30-50 percent from a smooth surface to a wire and retaining it on the wire. If the suction, for any reason, were to stop or be reduced, the fibrous web would continue with the smooth roller, which might result in shut-down and damage to the machine. The paper machine in accordance with U.S. Pat. No. 4,849,054 cannot be operated at the high speeds that are demanded today, because of the configuration of the press and the transfer point with a stationary suction pipe, around which the texturing wire runs with high friction between them.
A similar arrangement is shown in U.S. Pat. No. 4,834,838, particularly FIG. 9, where the fibrous web passes a suction opening so that it is drawn to the wire, whereby the surface facing the wire should acquire a wave-shaped pattern corresponding to the wire, while the other surface of the fibrous web should be smooth. The patent is concerned with the manufacture of fibrous tape base material of the type used in making masking tape, rather than soft structured paper. A foremost concern of the patent is imparting stretchability to the tape base material in the machine direction while making the tape surface smooth and attaining a thin caliper. Differences in speed between the wire and the opposite web-carrying element are used to make the web stretchable. The fibrous web has been dewatered before it reaches said suction opening, but no description is given of how this dewatering is effected in this specific embodiment. In any event, it is not apparent from this patent specification that a bulk should be recreated after pressing in a roller nip. The wave shape, limited to one surface, will be partially or completely destroyed during the subsequent contacts with different elements, such as drying cylinders and felts, although the stretchability achieved in the fibrous web is purportedly retained.
U.S. Pat. No. 5,411,636 describes the manufacture of soft paper, where the paper web is formed on a forming wire, pre-pressed in a double-felted press nip and transferred to a coarse-meshed wire. The paper web, while being carried by the coarse-meshed wire, is subjected to an abrupt vacuum pulse in a suction zone so that the paper web is drawn into the openings and depressions of the wire so that the paper web acquires an increased thickness and, thus, increased bulk. The coarse-meshed wire then carries the paper web to the drying cylinder. The double-felted press nip results in the dry solids content of the paper web after the press nip being relatively low, namely 25-30 percent. As no dewatering can be carried out in the nip at the drying cylinder, the dry solids content of the paper web when it is transferred to the drying cylinder is correspondingly low.
To increase the dry solids content of the paper web up to the drying cylinder without subjecting the paper web to extreme compressing forces in one or several press nips, the technique of through-blow drying is often used, as shown, for instance, in U.S. Pat. No. 3,301,746, U.S. Pat. No. 5,411,636, U.S. Pat. No. 5,667,636 (corresponding to WO 95/00706), U.S. Pat. No. 4,440,597, U.S. Pat. No. 5,364,504, U.S. Pat. No. 5,529,664, U.S. Pat. No. 3,994,771 (corresponding to SE-7605986-4), and U.S. Pat. No. 4,529,480. This technique produces a paper web with high bulk. A paper machine with through-blow drying does, however, entail high investment costs as well as high running costs, mainly with respect to energy consumption.